U.S. patent number 6,466,670 [Application Number 09/481,739] was granted by the patent office on 2002-10-15 for system for preventing playback of unauthorized digital video recordings.
This patent grant is currently assigned to NDS Limited. Invention is credited to Yishai Sered, Yossef Tsuria.
United States Patent |
6,466,670 |
Tsuria , et al. |
October 15, 2002 |
System for preventing playback of unauthorized digital video
recordings
Abstract
This invention discloses an anti-piracy system including video
representation signature apparatus for computing a forbidden
signature of a forbidden video representation, communication
apparatus for communicating the forbidden signature to a playing
device, and a playing device adapted to receive and play back a
recorded video representation, the playing device including
reception apparatus for receiving the forbidden signature
communicated by the communication apparatus, recorded video
representation signature apparatus for computing a signature of the
recorded video representation, and playback control apparatus
operative to prevent playback of the recorded video representation
if the computed signature of the recorded video representation
matches the forbidden signature communicated to the playing
device
Inventors: |
Tsuria; Yossef (Jerusalem,
IL), Sered; Yishai (Jerusalem, IL) |
Assignee: |
NDS Limited (Middlesex,
GB)
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Family
ID: |
11071534 |
Appl.
No.: |
09/481,739 |
Filed: |
January 11, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCTIL9900127 |
Mar 4, 1999 |
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Foreign Application Priority Data
Current U.S.
Class: |
380/202;
348/E7.06; 348/E5.004; 375/E7.089; 386/E5.004 |
Current CPC
Class: |
G06K
9/00711 (20130101); H04N 5/913 (20130101); H04N
7/162 (20130101); H04N 21/4627 (20130101); G06F
16/785 (20190101); H04N 19/467 (20141101); H04N
21/8352 (20130101); H04N 2005/91335 (20130101); H04N
2005/91342 (20130101) |
Current International
Class: |
H04N
5/00 (20060101); H04N 7/16 (20060101); H04N
7/26 (20060101); H04N 5/913 (20060101); H04N
007/167 () |
Field of
Search: |
;380/202,201,210,214,215,217,241,242 ;173/176,168
;705/51,57,58 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 367 585 |
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May 1990 |
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EP |
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0 651 554 |
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May 1995 |
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EP |
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0 715 241 |
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Jun 1996 |
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EP |
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WO 96/07272 |
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Mar 1996 |
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WO |
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WO 96/41468 |
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Dec 1996 |
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WO |
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WO 97/13248 |
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Apr 1997 |
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WO |
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WO 97/21162 |
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Jun 1997 |
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WO |
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WO 97/22206 |
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Jun 1997 |
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WO |
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WO 97/26732 |
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Jul 1997 |
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WO |
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WO 97/26733 |
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Jul 1997 |
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WO |
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WO 97/34391 |
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Sep 1997 |
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WO |
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WO 98/02864 |
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Jan 1998 |
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WO |
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WO 98/03014 |
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Jan 1998 |
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WO |
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Other References
Schneider, M. et al., "A Robust Content Based Digital Signature for
Image Authentication," Proceedings of the International Conference
on Image Processing, Sep. 1996, pp. 227-230, XP-002090178. .
Wolfgang, R. and Edward J. Delp, "Overview of Image Security
Techniques With Application in Multimedia Systems," Proceedings of
the SPIE, vol. 3228, 1998, pp. 297-308, XP-002104655 1998. .
Digimarc Corporation, Digimarc Watermarking Guide, 1997, pp. 1-18.
.
Digimarc Corporation, "Project Digilock--The Digital Content
Protection Solution for Copy Control and Play Control," Presented
by Macrovision Corporation and Digimarc Corporation, Fall
1997..
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Primary Examiner: Smithers; Matthew
Attorney, Agent or Firm: Ladas & Parry
Parent Case Text
This application is continuation of international application
number PCT IL 99/00127, filed Mar. 4, 1999, now pending.
Claims
What is claimed is:
1. A method for assigning a signature to a video representation,
the video representation comprising a plurality of frames, the
method comprising: choosing a chosen plurality of frames from among
the plurality of frames comprised in the video representation; for
each of the chosen plurality of frames, computing a frame
characteristic value, thus producing a plurality of frame
characteristic values; computing a function of the plurality of
frame characteristic values and assigning a result of the function
as the signature; communicating the signature to a playing device;
providing a recorded video representation to the playing device;
computing a signature of the recorded video representation; and
preventing playback of the video representation in the playing
device if the computed signature of the recorded video
representation matches the signature communicated to the playing
device.
2. A method according to claim 1 and wherein the function comprises
concatenation of the plurality of frame characteristic values.
3. A method according to claim 1 and wherein the video
representation comprises an MPEG representation, and each of the
chosen plurality of frames comprises an I-frame.
4. A method according to claim 1 and wherein the step of preventing
playback comprises: preventing playback of the video representation
in the playing device if the computed signature of the recorded
video representation is identical to the signature communicated to
the playing device.
5. A method according to claim 1 and wherein the step of preventing
playback comprises: employing a signature comparison method to
determine whether the computed signature of the recorded video
representation matches the signature communicated to the playing
device, and the signature comparison method includes determining
that a first signature and a second signature match even if the
first signature is not identical to the second signature.
6. A method according to claim 1 and wherein the step of computing
a frame characteristic value comprises: dividing the frame into a
plurality of regions; choosing one of the plurality of regions; and
computing a region characteristic value of the chosen region and
assigning the region characteristic value as the frame
characteristic value.
7. A method according to claim 6 and wherein the region
characteristic value comprises a function of average pixel value
for the region.
8. A method according to claim 7 and wherein the function of
average pixel value produces a 1-bit value.
9. A method according to claim 8 and wherein the function of
average pixel value produces a 1-bit value of "1" for a first one
of the chosen plurality of frames.
10. A method according to claim 6 and wherein the step of dividing
the frame into a plurality of regions comprises, for each frame in
the chosen plurality of frames, dividing the frame into a plurality
of regions each corresponding to one of the plurality of regions
into which every other frame of the chosen plurality of frames is
divided.
11. A method according to claim 10 and wherein the step of choosing
one of the plurality of regions comprises choosing, for each frame
in the chosen plurality of frames, a region corresponding to the
region chosen in every other frame of the chosen plurality of
frames.
12. A method according to claim 10 and wherein the step of choosing
one of the plurality of regions comprises choosing, for at least
one frame in the chosen plurality of frames, a region not
corresponding to a region chosen in at least one other frame of the
chosen plurality of frames.
13. A system for assigning a signature to a video representation,
the video representation comprising a plurality of frames, the
system comprising: frame selection apparatus for choosing a chosen
plurality of frames from among the plurality of frames comprised in
the video representation; a frame characteristic determination unit
operative, for each of the chosen plurality of frames, to compute a
frame characteristic value, thus producing a plurality of frame
characteristic values; signature apparatus for computing a function
of the plurality of frame characteristic values and assigning a
result of the function as the signature; and communication
apparatus for communicating the signature to a playing device,
wherein the playing device comprises: a receiving unit for
receiving a recorded video representation; signature apparatus for
computing a signature of the recorded video representation; and
playback control apparatus for preventing playback of the video
representation in the playing device if the computed signature of
the recorded video representation matches the signature
communicated to the playing device.
14. A method for assigning a signature to a video representation,
the video representation comprising a plurality of frames, the
method comprising: choosing a chosen plurality of frames from among
the plurality of frames comprised in the video representation; for
each of the chosen plurality of frames, computing a frame
characteristic value, thus producing a plurality of frame
characteristic values; computing a function of the plurality of
frame characteristic values and assigning a result of the function
as the signature; and communicating the signature to a playing
device, wherein the step of computing a frame characteristic value
comprises: dividing the frame into a plurality of regions; choosing
one of the plurality of regions; and computing a region
characteristic value of the chosen region and assigning the region
characteristic value as the frame characteristic value, and the
region characteristic value comprises a function of average pixel
value for the region, and the function of average pixel value
produces a 1-bit value.
15. A method according to claim 14 and wherein the function
comprises concatenation of the plurality of frame characteristic
values.
16. A method according to claim 14 and wherein the video
representation comprises an MPEG representation, and each of the
chosen plurality of frames comprises an I-frame.
17. A method according to claim 14 and also comprising: providing a
recorded video representation to the playing device; computing a
signature of the recorded video representation; and preventing
playback of the video representation in the playing device if the
computed signature of the recorded video representation matches the
signature communicated to the playing device, wherein the step of
preventing playback comprises: preventing playback of the video
representation in the playing device if the computed signature of
the recorded video representation is identical to the signature
communicated to the playing device.
18. A method according to claim 14 and also comprising: providing a
recorded video representation to the playing device; computing a
signature of the recorded video representation; and preventing
playback of the video representation in the playing device if the
computed signature of the recorded video representation matches the
signature communicated to the playing device, wherein the step of
preventing playback comprises: employing a signature comparison
method to determine whether the computed signature of the recorded
video representation matches the signature communicated to the
playing device, and the signature comparison method includes
determining that a first signature and a second signature match
even if the first signature is not identical to the second
signature.
19. A method according to claim 14 and wherein the function of
average pixel value produces a 1-bit value of "1" for a first one
of the chosen plurality of frames.
20. A method according to claim 14 and wherein the step of dividing
the frame into a plurality of regions comprises, for each frame in
the chosen plurality of frames, dividing the frame into a plurality
of regions each corresponding to one of the plurality of regions
into which every other frame of the chosen plurality of frames is
divided.
21. A method according to claim 20 and wherein the step of choosing
one of the plurality of regions comprises choosing, for each frame
in the chosen plurality of frames, a region corresponding to the
region chosen in every other frame of the chosen plurality of
frames.
22. A method according to claim 20 and wherein the step of choosing
one of the plurality of regions comprises choosing, for at least
one frame in the chosen plurality of frames, a region not
corresponding to a region chosen in at least one other frame of the
chosen plurality of frames.
23. A system for assigning a signature to a video representation,
the video representation comprising a plurality of frames, the
system comprising: frame selection apparatus for choosing a chosen
plurality of frames from among the plurality of frames comprised in
the video representation; a frame characteristic determination unit
operative, for each of the chosen plurality of frames, to compute a
frame characteristic value, thus producing a plurality of frame
characteristic values; signature apparatus for computing a function
of the plurality of frame characteristic values and assigning a
result of the function as the signature; and communication
apparatus for communicating the signature to a playing device,
wherein the frame characteristic determination unit is operative to
compute the frame characteristic value by: dividing the frame into
a plurality of regions; choosing one of the plurality of regions;
and computing a region characteristic value of the chosen region
and assigning the region characteristic value as the frame
characteristic value, and the region characteristic value comprises
a function of average pixel value for the region, and the function
of average pixel value produces a 1-bit value.
24. An anti-piracy method comprising: computing a forbidden
signature of a forbidden video representation; communicating the
forbidden signature to a playing device; providing a recorded video
representation to the playing device; computing a signature of the
recorded video representation; and preventing playback of the
recorded video representation in the playing device if the computed
signature of the recorded video representation matches the
forbidden signature communicated to the playing device.
25. A method according to claim 24 and also comprising: storing the
forbidden signature at the playing device; and retrieving the
forbidden signature before performing the preventing playback
step.
26. An anti-piracy system comprising: video representation
signature apparatus for computing a forbidden signature of a
forbidden video representation; communication apparatus for
communicating the forbidden signature to a playing device; and a
playing device adapted to receive and play back a recorded video
representation, the playing device comprising: reception apparatus
for receiving the forbidden signature communicated by the
communication apparatus; recorded video representation signature
apparatus for computing a signature of the recorded video
representation; and playback control apparatus operative to prevent
playback of the recorded video representation if the computed
signature of the recorded video representation matches the
forbidden signature communicated to the playing device.
27. A system according to claim 26 and wherein the reception
apparatus is operative to receive the forbidden signature during
playback of a non-forbidden recorded video representation.
28. A system according to claim 27 and wherein the reception
apparatus is also operative to receive an authorization message
authorizing playback of the non-forbidden recorded video
representation, and the authorization message comprises the
forbidden signature.
29. A playing device adapted to receive and play back a recorded
video representation the playing device comprising: reception
apparatus for receiving a forbidden signature of a forbidden video
representation; recorded video representation signature apparatus
for computing a signature of the recorded video representation; and
playback control apparatus operative to prevent playback of the
recorded video representation if the computed signature of the
recorded video representation matches the forbidden signature
received by the playing device.
30. Apparatus according to claim 29 and also comprising: forbidden
signature storage apparatus operative to store the forbidden
signature, and wherein the playback control apparatus receives the
forbidden signature from the forbidden signature storage apparatus.
Description
FIELD OF THE INVENTION
The present invention relates to anti-piracy systems for
discouraging and/or preventing theft of items such as electronic
representations, particularly electronic video representations.
BACKGROUND OF THE INVENTION
Anti-piracy methods and apparatus for discouraging and/or
preventing theft of items such as electronic representations are
well known in the art. Prominent among the methods is a class of
methods known collectively as watermarking. In watermarking
methods, a watermark signal is typically added to an electronic
representation to be protected. In such methods the added signal
typically carries information identifying the owner of the
electronic representation, and may carry additional information
such as an identification of a buyer of a copy of the electronic
representation. The added signal is, in some case, visible but in
many cases the added signal is disguised so that a potential thief
or pirate could find the signal only with great difficulty. Another
preferred attribute of watermarking methods is that alterations of
the picture, such as adding noise, not erase the watermark.
Typical watermarking methods are described in the following:
Digimarc.RTM. Watermarking Guide, 1997, Digimarc Corporation, 521
SW 11th Ave., Suite 200, Portland, OR 97205; Project DigiLock, The
Digital Content Protection Solution for Copy Control and Play
Control, presented by Macrovision Corporation and Digimarc
Corporation, Fall, 1997; European Patent Application EP 0 651 554
A1, assigned to Eastman Kodak Company; PCT Patent Application WO
96/41468, assigned to Macrovision Corporation; PCT Patent
Application WO 97/13248, assigned to Philips Electronics N.V.; PCT
Patent Application WO 97/22206, assigned to Philips Electronics
N.V.; PCT Patent Application 97/26732, assigned to The Dice
Company; PCT Patent Application 97/26733, assigned to The Dice
Company; PCT Patent Application 97/34391, assigned to Leighton; PCT
Patent Application 98/02864, assigned to The Dice Company; PCT
Patent Application 98/03014, assigned to Philips Electronics N.V.;
U.S. Pat. No. 5,606,609 to Houser et al; U.S. Pat. No. 5,607,188 to
Bahns et al; U.S. Pat. No. 5,636,292 to Rhoads; U.S. Pat. No.
5,659,726 to Sandford, II et al; U.S. Pat. No. 5,664.018 to
Leighton; and U.S. Pat. No. 5,687,236 to Moskowitz et al;
The disclosures of all references mentioned above and throughout
the present specification are hereby incorporated herein by
reference.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved anti-piracy
system. In the present invention a video representation, including
a plurality of frames, is assigned a signature, typically a
signature based on frame characteristic values which represent
characteristics visible to a viewer of the video representation.
Thus, an attempt to alter the video representation in order to
alter the signature such an attempt typically being analogous to
well-known methods of altering a video representation in order to
obliterate a watermark would alter the visible characteristics of
the video representation.
A particular method of computing such a signature, based on
selecting a plurality of frames and dividing each frame into a
plurality of regions, is also provided. In this method, a
particular region is chosen from each frame and some
characteristic, such as average pixel value in the region, is used
to characterize the frame. A signature is then computed based on
the plurality, of characterizing values from the plurality of
frames.
Preferably, the signature is transmitted to playing devices which
will then reject, by refusing to play, any recording having the
transmitted signature. Typically, the playing device will attempt
to match a computed signature of a recording with the transmitted
signature.
The term "match", as used throughout the present specification and
claims in referring to comparison of signatures or a result of such
comparison, is used in a broad sense to include not only a
determination that two signatures are identical but also any
analogous determination, using any appropriate signature mechanism,
which establishes that the two signatures represent two acts of
signing identical material. It is appreciated that there may be
appropriate signature mechanisms for which two such matching
signatures are not actually identical. For example and without
limiting the generality of the foregoing in some signature methods
based on public/private key systems, which are well known in the
art, two such matching signatures may not be actually
identical.
It is appreciated that the system of the present invention is
particularly applicable in a case where all playing devices are
built to conform to the system. It is also appreciated that the
system of the present invention is particularly applicable to
preventing the distribution of pirate copies of video material
which has no legitimate distribution channel. One example of such
video material is a master copy of an as-yet unreleased movie.
Although the present invention relates especially to video
representations it is appreciated that similar methods could be
applied in the case of other electronic representations such as
audio representations.
There is thus provided in accordance with a preferred embodiment of
the present invention a method for assigning a signature to a video
representation, the video representation including a plurality of
frames, the method including choosing a chosen plurality of frames
from among the plurality of frames included in the video
representation, for each of the chosen plurality of frames,
computing a frame characteristic value, thus producing a plurality
of frame characteristic values, and computing a function of the
plurality of frame characteristic values and assigning a result of
the function as the signature.
Further in accordance with a preferred embodiment of the present
invention the function includes concatenation of the plurality of
frame characteristic values.
Still further in accordance with a preferred embodiment of the
present invention the video representation includes an MPEG
representation, and each of the chosen plurality of frames includes
an I-frame.
Additionally in accordance with a preferred embodiment of the
present invention the method also includes communicating the
signature to a playing device.
Moreover in accordance with a preferred embodiment of the present
invention the method also includes providing a recorded video
representation to the playing device, computing a signature of the
recorded video representation, and preventing playback of the video
representation in the playing device if the computed signature of
the recorded video representation matches the signature
communicated to the playing device.
Further in accordance with a preferred embodiment of the present
invention the step of preventing playback includes preventing
playback of the video representation in the playing device if the
computed signature of the recorded video representation is
identical to the signature communicated to the playing device.
Still further in accordance with a preferred embodiment of the
present invention the step of preventing playback includes
employing a signature comparison method to determine whether the
computed signature of the recorded video representation matches the
signature communicated to the playing device wherein the signature
comparison method includes determining that a first signature and a
second signature match even if the first signature is not identical
to the second signature.
Additionally in accordance with a preferred embodiment of the
present invention the step of computing a frame characteristic
value includes dividing the frame into a plurality of regions,
choosing one of the plurality of regions, and computing a region
characteristic value of the chosen region and assigning the region
characteristic value as the frame characteristic value.
Moreover in accordance with a preferred embodiment of the present
invention the region characteristic value includes a function of
average pixel value for the region.
Further in accordance with a preferred embodiment of the present
invention the function of average pixel value produces a 1-bit
value.
Still further in accordance with a preferred embodiment of the
present invention the function of average pixel value produces a
1-bit value of "1" for a first one of the chosen plurality of
frames.
Additionally in accordance with a preferred embodiment of the
present invention the step of dividing the frame into a plurality
of regions includes, for each frame in the chosen plurality of
frames, dividing the frame into a plurality of regions each
corresponding to one of the plurality of regions into which every
other frame of the chosen plurality of frames is divided.
Moreover in accordance with a preferred embodiment of the present
invention the step of choosing one of the plurality of regions
includes choosing, for each frame in the chosen plurality of
frames, a region corresponding to the region chosen in ever, other
frame of the chosen plurality of frames.
Further in accordance with a preferred embodiment of the present
invention the step of choosing one of the plurality of regions
includes choosing, for at least one frame in the chosen plurality
of frames a region not corresponding to a region chosen in at least
one other frame of the chosen plurality of frames.
There is also provided in accordance with another preferred
embodiment of the present invention an anti-piracy method including
computing a forbidden signature of a forbidden video
representation, communicating the forbidden signature to a playing
device, providing a recorded video representation to the playing
device, computing a signature of the recorded video representation
and preventing playback of the recorded video representation in the
playing device if the computed signature of the recorded video
representation matches the forbidden signature communicated to the
playing device.
Further in accordance with a preferred embodiment of the present
invention the method also includes storing the forbidden signature
at the playing device, and retrieving the forbidden signature
before performing the preventing playback step.
There is also provided in accordance with another preferred
embodiment of the present invention a system for assigning a
signature to a video representation, the video representation
including a plurality of frames, the system including frame
selection apparatus for choosing a chosen plurality of frames from
among the plurality of frames included in the video representation,
a frame characteristic determination unit operative, for each of
the chosen plurality of frames, to compute a frame characteristic
value, thus producing a plurality of frame characteristic values,
and signature apparatus for computing a function of the plurality
of frame characteristic values and assigning a result of the
function as the signature.
There is also provided in accordance with another preferred
embodiment of the present invention an anti-piracy system including
video representation signature apparatus for computing a forbidden
signature of a forbidden video representation, communication
apparatus for communicating the forbidden signature to a playing
device, and a playing device adapted to receive and play back a
recorded video representation, the playing device including
reception apparatus for receiving the forbidden signature
communicated by the communication apparatus, recorded video
representation signature apparatus for computing a signature of the
recorded video representation and playback control apparatus
operative to prevent playback of the recorded video representation
if the computed signature of the recorded video representation
matches the forbidden signature communicated to the playing
device.
Further in accordance with a preferred embodiment of the present
invention the reception apparatus is operative to receive the
forbidden signature during playback of a non-forbidden recorded
video representation.
Still further in accordance with a preferred embodiment of the
present invention the reception apparatus is also operative to
receive an authorization message authorizing playback of the
non-forbidden recorded video representation, and the authorization
message includes the forbidden signature.
There is also provided in accordance with another preferred
embodiment of the present invention a playing device adapted to
receive and play back a recorded video representation, the playing
device including reception apparatus for receiving a forbidden
signature of a forbidden video representation, recorded video
representation signature apparatus for computing a signature of the
recorded video representation, and playback control apparatus
operative to prevent playback of the recorded video representation
if the computed signature of the recorded video representation
matches the forbidden signature received by the playing device.
Further in accordance with a preferred embodiment of the present
invention the playing device also includes forbidden signature
storage apparatus operative to store the forbidden signature, and
wherein the playback control apparatus receives the forbidden
signature from the forbidden signature storage apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully
from the following detailed description, taken in conjunction with
the drawings in which:
FIG. 1 is a simplified pictorial illustration of an anti-piracy
system constructed and operative in accordance with a preferred
embodiment of the present invention;
FIG. 2 is a simplified flowchart illustration of a preferred method
of operation of the system of FIG. 1;
FIG. 3 is a simplified flowchart illustration of a preferred
implementation of steps 215 and 230 of FIG. 2;
FIG. 4 is a simplified flowchart illustration of a preferred
implementation of step 260 of FIG. 3;
FIG. 5 is a simplified pictorial illustration of a frame of a video
representation, useful in understanding the method of FIG. 4;
and
FIG. 6 is a simplified flowchart illustration of a preferred
implementation of step 285 of FIG. 5.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Reference is now made to FIG. 1 which is a simplified pictorial
illustration of an anti-piracy system constructed and operative in
accordance with a preferred embodiment of the present invention.
The system of FIG. 1 preferably comprises, typically in a central
security station 100, a signature computation device 110 The
signature computation device 110, preferably implemented in a
combination of hardware and software as is well known in the art,
is typically operative to receive a forbidden video representation
120 as input and to produce a forbidden signature 130, typically a
digital signature, as output.
The forbidden video representation 120 may be in any appropriate
format, although it is appreciated that a digital format,
especially a standard digital format such as MPEG, may be
preferred. The forbidden video representation 120 may be provided
to the signature computation device 110 in any appropriate form
such as, for example, one of the following: a video cassette; a
video disc such as a digital video disk (DVD): or an electronic
stream whether carried by wire or wirelessly. The forbidden video
representation 120 is shown in FIG. 1 as a video cassette by way of
example only, and this example is not meant to be limiting.
It is appreciated that the apparatus and methods of the present
invention may also be adapted, by a reasonably skilled person of
the art, to operate with other types of digital representations
other than video representations such as, for example, audio
representations. The example of a video representation is used
throughout the present specification and claims by way of example
only, and is not mean to be limiting. Whenever a term which is
particularly associated with video, such as, for example, "frame"
or "pixel", is used, it is appreciated that, in the case of other
types of digital representations the digital representation may be
divided into sub-units and sub-sub-units according to any
appropriate rule, the sub-units and sub-sub-units then functioning
in the place of frames and pixels, respectively.
The signature computation device 110 is preferably operative to
compute a signature, such as a digital signature, of the forbidden
video representation 120. Preferably, the method used by the
signature computation device 110 is highly sensitive to one or more
perceived visual characteristics of the forbidden video
representation 120, that is, to visual characteristics which would
be perceived by a typical viewer of the forbidden video
representation 120.
Typically, the signature produced by the signature computation
device 110 will be some appropriate function of the perceived
visual characteristics of the forbidden video representation 120.
Hence, the signature will be highly dependent on one or more
perceived visual characteristics and any attempt by an unauthorized
person to alter the signature computed by the signature computation
device 110 would likely necessitate changing characteristics of the
forbidden video representation 120 which changes would be perceived
by a typical user thereof. Furthermore, the signature produced by
the signature computation device 110 is preferably highly
input-dependent, in the sense that two different video
representations provided as input should cause two different
signatures to be produced as output, preferably in all such
cases.
A preferred method of operation of the signature computation device
110 is described in more detail below with reference to FIG. 3.
The central security station 100 typically also comprises
conventional communication apparatus (not shown) operatively
associated with the signature computation device 110 and operative
to transmit, typically via broadcast transmission, the forbidden
signature 130 via any appropriate communications channel such as a
satellite communications channel 140.
It is appreciated that a subcombination of the system of FIG. 1
including the apparatus comprised in the central security station
100 may by itself comprise a preferred embodiment of the present
invention.
The system of FIG. 1 also preferably comprises, typically at a
consumer location 150 a playback device 160. Although a single
consumer location 150 and a single playback device 160 are shown in
FIG. 1, it is appreciated that the consumer location 150 may
alternatively include a plurality of playback devices 160 and the
system of FIG. 1 may, and typically will, include a multiplicity of
consumer locations 150, each including at least one playback device
160. The depictions of a single consumer location 150 and of a
single playback device 160 in FIG. 1 are for purposes of simplicity
of description and are not meant to be limiting.
The playback device 160 is preferably adapted to receive and
playback for consumer viewing a recorded video representation 170,
as is well-known in the art, and preferably comprises conventional
components (not shown) for carrying out this purpose. The playback
device 160 also preferably comprises conventional communication
apparatus (not shown) operative to receive transmissions from the
satellite communications channel 140.
The playback device 160 also typically comprises the following
components, typically implemented in a combination of hardware and
software: a forbidden signature storage unit 180, operatively
associated with the conventional communication apparatus (not
shown) and operative to receive the forbidden signature 130
therefrom, to store the forbidden signature 130 and, preferably,
other similar signatures which may be broadcast from time to time
and to recall for further processing the stored forbidden signature
130; a signature computation device 10, preferably similar or
identical in function to the signature computation device 110
comprised in the central security station 100 and operative to
receive as input the recorded video representation 170 and to
compute a recording signature 185 therefrom, according to a method
producing the same result from the same input as the signature
computation device 110 comprised in the central security station
100; a comparator 190 operatively associated with the signature
computation device 110 and with the forbidden signature storage
unit 180 and operative to receive therefrom the recording signature
185 and the forbidden signature 130 and to provide a result, based
on comparison of the recording signature 185 to the forbidden
signature 130, indicating whether the two signatures 185 and 130
match; and a playback prevention device operative, if the result
produced by the comparator 190 indicates that the recording
signature 185 is the same as the forbidden signature 130, to
prevent playback of the recorded video representation 170 by the
playback device 160, using any appropriate means for preventing
playback as is well-known in the art.
Some or all of the signature computation device 110, the forbidden
signature storage unit 180, the comparator 190, and the playback
prevention device 200 may be implemented in one or more integrated
circuit devices or one or more microprocessors, as is well known in
the art.
The operation of the system of FIG. 1 is now briefly described. A
forbidden video representation 120, the playing of which on
consumer devices is to be prevented, is preferably chosen and
presented as input to the signature computation device 110. As
explained above, the forbidden video representation 120 may be in
any appropriate format, chosen to be compatible with one or more
formats accepted by the signature computation device 110 and
typically comprises a video work, such as a copyrighted video work,
which is unreleased or otherwise unavailable to the public.
The signature computation device 10 preferably computes a forbidden
signature 130 as described above. The forbidden signature 130 is
then preferably transmitted via the satellite communications
channel 140 to the playback device 160. At the playback device 160,
the forbidden signature 130 or an appropriate derived
representation thereof such as, for example, an appropriate hash
thereof, is typically stored in the forbidden signature storage
unit 180. It is appreciated that the forbidden signature 130 or the
appropriate derived representation may also be used immediately,
without storage in the forbidden signature storage unit 180; in
such a case, the forbidden signature storage unit 180 may be
optional.
As explained above, upon presentation of a recorded video
representation 170 for playback by the playback device 160 a
recording signature 185 of the recorded video representation 170 is
preferably computed and compared to the stored forbidden signature
130 by the comparator 190.
Preferably, if the signatures 130 and 185 do not match, playback of
the recorded video representation 170 is allowed. Preferably, if
the signatures 130 and 185 do match, indicating that the recorded
video representation 170 includes a forbidden video representation,
playback of the recorded video presentation 170 is forbidden.
Thus, the system of FIG. 1 provides anti-piracy protection against
pirate copies of the forbidden video representation 120.
It is appreciated that the forbidden signature storage unit 180 may
be operative to store a plurality of signatures 130 associated with
a plurality of different forbidden video representations 1220,
including variant representations of a single forbidden video
representation 120. For example, a pirate might create such a
variant representation by attempting to alter the signature of a
pirated recorded video representation 170 by changing the content
thereof such as, for example, by deleting a small portion such as a
small beginning portion thereof It is appreciated that an effective
anti-piracy defense against such a measure might comprise obtaining
such an altered video representation and using the altered video
representation as input to the signature computation device 110 in
place of the forbidden video representation 120, thus causing the
altered video representation to also be forbidden. It is further
appreciated that a beginning of a particular scene may be
identified using methods well known in the art, and signature
computation may be based on the beginning of the particular scene
rather than the beginning of the recorded video representation 170,
thus also providing an effective anti-piracy defense against
deletion of a small beginning portion of the recorded video
representation 170.
It is further appreciated that it might be desirable to cancel the
forbidden signature 130 previously broadcast, thus allowing
playback of a recorded video representation 170 having the same
signature as the forbidden video representation 120. This might be
the case, for example, when legitimate copies of the previously
unreleased forbidden video representation 120 are released. In such
a case, it would be desirable to broadcast a special message
canceling the forbidden signature 130, in response to which the
playback device 160 would erase the forbidden signature 130 from
the forbidden signature storage unit 180, thus permitting playback.
Methods for ensuring the legitimacy of such a message, including
requiring that such a message be cryptographically signed, are
well-known in the art, particularly in the art of pay television
where authorization and restriction messages typically require
authentication. It is further appreciated that, because of security
considerations, it may be preferable to employ such methods for
ensuring legitimacy both in broadcast of a special message and in
broadcast of the forbidden signature 130 as described above.
It is still further appreciated that appropriate methods are
preferably employed to help ensure delivery of the forbidden
signature 130 despite piracy attempts. For example, the forbidden
signature 130 may be delivered during playback of a non-forbidden
recorded video representation, the forbidden signature 130
typically being comprised in an authorization message authorizing
playback of the non-forbidden recorded video representation. Such
authorization messages are well-known in the art of television
conditional access.
Reference is now made to FIG. 2. which is a simplified flowchart
illustration of a preferred method of operation of the system of
FIG. 1. The method of FIG. 2 preferably comprises the following
steps:
A forbidden signature of a forbidden video representation is
computed (step 215). As described above with reference to FIG. 1,
the signature computation of step 215 is preferably based on
visible characteristics of the forbidden video representation and
is preferably sensitive to visible differences in the forbidden
video representation, while being insensitive to invisible
differences in the forbidden video representation. A preferred
implementation of step 215 is described in more detail below with
reference to FIG. 3, but it is appreciated that any other
appropriate implementation may alternatively be used.
The forbidden signature computed in step 215 is communicated to a
playing device (step 220). Typically at a later time, a recorded
video representation is provided to the playing device for playback
(step 225). A signature of the recorded video representation is
computed (step 230); preferably, the computation in step 230 is
similar to that in step 215, as described above, in that the
computation in step 230 is preferably either identical to that in
step 215 or so designed as to always produce, from a given input,
the same output produced by the computation of step 215.
A check is made as to whether the computed signature of the
recorded video representation matches the forbidden signature
communicated to the playing device (step 235); if not, playback of
the recorded video representation is preferably allowed (step 240).
If, however, the forbidden signature matches the computed signature
of the recorded video representation, playback of the recorded
video representation is preferably forbidden (step 245).
It may be preferable in step 235 to require an exact match between
the signatures being compared in order for a match to be determined
by, step 235, alternatively, any appropriate function of similarity
might be applied to determine that the signatures being compared
are sufficiently similar for a match to be determined by step 235.
It is appreciated that an appropriate function of similarity might
be used in a case where a signature method used in steps 215 and
230 is designed to produce similar signatures for similar inputs,
with the function of similarity of step 235 being chosen
accordingly.
Reference is now made to FIG. 3, which is a simplified flowchart
illustration of a preferred implementation of steps 215 and 230 of
FIG. 2. The method of FIG. 3 preferably includes the following
steps:
A chosen plurality of frames is chosen from among the plurality of
frames comprised in the forbidden video representation (250). The
chosen plurality of frames may be chosen according to some fixed
rule, such as the first n frames of the video representation, where
n is a predetermined number such as, for example, 32.
Alternatively, n frames other than the first n frames may be
chosen. Further alternatively, n may be a variable parameter,
typically chosen according to some appropriate predetermined method
accepting one or more characteristics of the forbidden video
representation as input and producing n as output, and typically
varying from one forbidden video representation to another
according to any appropriate rule.
It is appreciated that, particularly in the case of compressed
digital formats of video representation, certain frames may include
more information about what is visible to a viewer than other
frames, and choosing from those certain frames to make up the
chosen plurality of frames would be preferable to choosing from
other frames. For example, and without limiting the generality of
the foregoing, it is well-known in the art that, in an MPEG video
representation, I-frames include full frame information and thus
include more information about what is visible to a viewer than do
P-frames and B-frames, which represent differences between frames
rather than full frame information. Therefore, in a case where the
forbidden video representation comprises an MPEG video
representation, it would be preferable to choose the chosen
plurality of frames from among I-frames comprised in the MPEG video
representation.
It is further appreciated that, in the case of other compressed
digital formats such as texture coding techniques using DCT blocks,
as is well-known in the art, other appropriate information, such as
DC coefficients of DCT blocks, may alternatively be used, in place
of I-frames in an MPEG representation. Similarly, in a format using
wavelets, as is well-known in the art, coefficients of the lowest
frequency wavelet sub-band might be used.
A plurality of frame characteristic values is produced by
performing an appropriate operation on each of the chosen plurality
of frames (step 255); the appropriate operation preferably
comprises computing a frame characteristic value for each of the
chosen plurality of frames (step 260); alternatively, a similar
method may be employed on subsequences of the chosen plurality of
frames rather than on individual ones of the chosen plurality of
frames. In step 260 a method of computing the frame characteristic
value is preferably chosen to produce the qualities of sensitivity
to changes in the frame described above with reference to step 215
of FIG. 2. Without limiting the generality of the foregoing, a
preferred implementation of step 260 is described more fully below
with reference to FIG. 4.
A function of the plurality of frame characteristic values is
computed and the result of computing the function is assigned as
the signature (step 265). Typically, the function of step 265
comprises concatenation of the plurality of frame characteristic
values. The function of step 265 may also comprise encrypting
and/or digitally signing the concatenation, as described above with
reference to FIG. 1. Alternatively, any other appropriate function
may be used.
Reference is now made to FIG. 4, which is a simplified flowchart
illustration of a preferred implementation of step 260 of FIG. 3.
The method of FIG. 4 preferably includes the following steps:
Each frame is divided into a plurality of regions (step 270).
Reference is now additionally made to FIG. 5, which is a simplified
pictorial illustration of a frame of a video representation, useful
in understanding the method of FIG. 4. In FIG. 5 a frame 272 is
shown divided, for purposes of computation into a plurality of
regions 274.
One of the plurality of regions, such as a chosen region 276 of
FIG. 5, is chosen from among the plurality of regions 274 of FIG. 5
(step 285). It is appreciated that any of a wide variety of methods
might be used for determining which of the plurality of regions 274
is chosen as the chosen region 276, and that the method used for
choosing in step 285 may depend on a function used in step 290,
described below. One possible method for choosing is as
follows:
Typically, the frame 272 of FIG. 5 comprises a multiplicity of
pixels (not shown), as is well-known in the art. Each pixel
typically has a value such as, for example, an integer value
between 0 and 255 inclusive. Depending on whether the frame 272
comprises a color frame, a grayscale frame, or some other type of
frame, the meaning of each of the possible pixel values varies
accordingly, as is well-known in the art.
An average pixel value is computed over all pixels of the frame
272, resulting in a frame average pixel value (FAPV). One or more
of the plurality of regions 274 is examined, and a region average
pixel value (RAPV) is computed for each examined region. Any of the
examined regions for which the RAPV is greater than the FAPV is
chosen as the chosen region 276.
Reference is now additionally made to FIG. 6, which is a simplified
flowchart illustration of a preferred implementation of step 285 of
FIG. 5. The method of FIG. 6 is self-explanatory in light of the
above discussion.
A region characteristic value of the chosen region is computed and
assigned as the frame characteristic value (step 290). One possible
example of a method of computing region characteristic value,
compatible with the method of FIG. 6 as described above, is
computing the RAPV of the region and assigning a one-bit region
characteristic value of "1" if the RAPV is greater than the FAPV,
and assigning a value of 0.
It is appreciated that, in case the method of FIG. 6 is used along
with the RAPV method for step 290, step 290 produces a value of 1
as the frame characteristic value of the first frame of the chosen
plurality of frames of step 250 of FIG. 3, described above. In a
case where the function of step 265 of FIG. 3 is a concatenation
function, as described above, the first bit of the signature
computed by step 265 of FIG. 3 will be a "1"bit, which may be
preferred.
It is appreciated that various features of the invention which are,
for clarity, described in the contexts of separate embodiments may
also be provided in combination in a single embodiment. Conversely,
various features of the invention which are, for brevity, described
in the context of a single embodiment may also be provided
separately or in any suitable subcombination.
It will be appreciated by persons skilled in the art that the
present invention is not limited by what has been particularly
shown and described hereinabove. Rather the scope of the invention
is defined only by the claims which follow.
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